Process for treating wells with viscous epoxy-resin-forming solutions

ABSTRACT

A well treating process in which a granular mass is consolidated by contacting it with an epoxy resin-forming solution that precipitates a self-curing partially-cured resin, is improved by using such a solution that contains a viscosity-increasing amount of an otherwise substantially inert oil-soluble polymer.

This is a division of application Ser. No. 852,175, filed Nov. 16, 1977,now U.S. Pat. No. 4,113,015, Sept. 12, 1978.

BACKGROUND OF THE INVENTION

The invention relates to: consolidating or strengthening unsolidated orpoorly consolidated subterranean reservior formations; consolidatingsand or gravel packs within wellbores; or consolidating masses ofpropping particles with hydraulically-induced fractures in subterraneanearth formations.

Numerous processes have been previously proposed for testing wells withepoxy resin-forming solutions in order to consolidate masses of sand orgravel in or around the boreholes of wells. The I. H. Havenaar and F.Meijs U.S. Pat. No. 3,294,166 proposes consolidations with an epoxyresin-forming solution from which a self-curing partially cured resin isprecipitated. The E. A. Richardson U.S. Pat. No. 3,339,633 proposesinjecting a relatively concentrated solution of resin-forming componentsfollowed by at least an equal volume of over-flushing liquid, which isimmiscible with the resin-forming components but is miscible with thesolvent for the resin-forming components, in order to provide atreatment that is relatively unaffected by the presence of clay-sizedsolids within the interstices of the granular mass to be consolidated.The E. H. Bruist, T. W. Hamby, T. A. Simon and R. N. Tuttle U.S. Pat.No. 3,621,915 (and various subsequent patents, such as U.S. Pat. Nos.3,857,444; 3,867,986 and 3,878,893) propose forming resin-consolidatedsand or gravel packs by injecting slurries of particles that are createdwith a self-curing, partially-cured epoxy resin (which can bepre-applied or can be adsorbed during the injection) suspended in acarrier liquid having some but limited miscibility with a polar liquidsolvent for the resin-forming components.

SUMMARY OF THE INVENTION

The present invention relates to an improved process for treating a wellby injecting, into the well and into any fluid-containing permeableearth formations encountered by the well, an epoxy-resin-formingsolution from which a self-curing partially-cured resin is precipitated.The improvement comprises dissolving in the resin-forming solution akind and amount of a viscosity-increasing oil-soluble polymeric materialthat increases the effective viscosity of the solution to more than thatof the fluid in the well or earth formation encountered by the wellwithout significantly affecting the resin forming and precipitatingproperties of the solution.

The present invention also relates to an epoxy-resin-forming solutionthat consists essentially of (A) from about 5-30% by volume of a mixtureof at least one epoxy resin having more than one vicinal epoxy group permolecule and at least one amine capable of acting as a curing agent forthat resin dissolved in a liquid mixture of aromatic and non-aromatichydrocarbons containing sufficient aromatics to keep an intermediateform of a self-curing partially-cured resin in solution throughout thetime required to pump the resin-forming solution into a granular mass ofmaterials to be treated in or around a subterranean portion of theborehole of a well and (B) also dissolved in the resin-forming solutiona kind and amount of oil-soluble polymeric material that provides aneffective or apparent viscosity of from about 1-150 centipoises (asmeasured at room temperature, at a shear rate of 51 reciprocal secondsin a Fann viscometer) without significantly affecting the resin-formingand precipitating properties of the solution.

The present invention also relates to a well treating process foremplacing and consolidating granular particles within a borehole of awell or within fractures that communicate with a well. This is done byinjecting into the borehole or fractures a suspension of the granularparticles in a relatively viscous epoxy-resin-forming solution of thetype described above. As will be apparent to those skilled in the art,whenever such a suspension is injected into a wellbore or fracturewithin a permeable earth formation, at least some epoxy-resin-formingsolution will be injected into a fluid-containing permeable earthformation.

DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic perspective view of a transparent box arranged forvisually observing the flow of fluids.

FIGS. 2-5 are illustrations of the boundary lines between various fluidsbeing displaced into and displaced from that box at various stages ofthe displacements.

DESCRIPTION OF THE INVENTION

This invention is, at least in part, premised on the discovery that aviscosity increasing amount of an oil-soluble polymeric material can bedissolved in an epoxy-resin-forming solution of the type from which aself-curing partially-cured resin is precipitated, without any unduealteration of either (a) the initial precipitation time, at which aself-curing partially-cured resin is precipitated, or (b) the capabilityof the resin-forming solution to consolidate a granular mass into acoherent structure of relatively high compressive strength. Because ofthat discovery it became possible to materially increase the effectiveviscosity of such a resin-forming solution with respect to thepreviously known resin-forming solutions that provided relatively highcompressive strengths. Such previously known solutions were nearly aslow viscous as water, e.g., about 0.74 centipoise at 60° C. With thecapability of increasing the effective viscosity of the resin-formingsolution it became possible to increase the effective viscosity of eachof a series of pre-flush fluids without creating an adverse ratio ofmobility between the last pre-flush fluid and the resin-formingsolution.

In various respects, the present invention involves an improvement ofthe process described in U.S. Pat. No. 3,294,166 for treating afluid-containing permeable earth formation with an epoxy-resin-formingsolution from which a self-curing partially-cured resin is precipitated.The disclosures of U.S. Pat. No. 3,294,166 (which is hereafter referredto as the 166 patent) are incorporated herein by cross-reference.

The process of the 166 patent has been used for consolidatingunconsolidated reservoir sands in numerous West African and U.S. oilfields. Experience has indicated that where failures have beenencountered they may have been due to unstable displacements ofrelatively viscous crude oils by relatively low viscosity resin-formingsolutions. An unfavorable mobility ratio may have resulted in leaving asignificant amount of reservoir oil within portions of the reservoirinterval to be consolidated. It is known that a relatively high oilsaturation may cause the consolidation to be weak or substantiallynon-existant. The present invention is particularly useful forconsolidating any unconsolidated or poorly consolidated reservoir thatcontains fluid having an effective viscosity which is greater than about1 centipose at the reservoir temperature.

From general reservoir engineering experience it is known that stableand effective displacements of crude oil and water can be achieved byusing, respectively, oil-miscible and water-miscible fluids havingeffective viscosities at least about equaling those of the fluids beingdisplaced. In particularly suitable well treatments utilizingepoxy-resin-forming solutions that precipitate self-curingpartially-cured resins, it is desirable to inject a sequence of fourfluids that each have a higher effective viscosity or lower mobilitythan the fluid being displaced, i.e.: (1) an oil solvent, such as dieseloil, for removing oil; (2) a fluid that is mutually miscible with oiland water, such as isopropyl alcohol, for removing water; (3) anoil-miscible spacer fluid, such as a mixture of diesel oil and anaromatic hydrocarbon, for removing the mutually-miscible fluid; and (4)the resin-forming solution. For example, in an oil-containing reservoirin which the effective viscosity of the oil is about three centipoisesthe effective viscosities of the injected fluids (at the reservoirtemperature) can advantageously be: about 3 for the oil solvent fluid:about 6 for the oil-and-water-miscible fluid; about 12 for theoil-miscible spacer fluid; and about 12 for the resin-forming solution.

In "remedial" sand control treatments, in addition to providing aneffective consolidation of the oil-bearing reservoir sand, it isdesirable to repack portions of the formation from which sand has beenwashed out during drilling or during the production of fluid from thereservoir. In prior remedial treatments, different types of sand orgravel slurries have been developed using different types of resins,different gravel concentrations, different carrying fluids, anddifferent viscosities. In general, such sand or gravel slurries containa self-curing liquid resin which is precoated onto the packed particlesor is adsorbed on them while the slurry is being prepared or pumped intothe zone to be treated. It is intended that, after the resin-coatedparticles have been transported into the void to be filled, the resinouscoatings will undergo some deformation as the particles are pressedtogether, and then cure to consolidate the particles in place. But, inusing such slurries, problems have been encountered.

A particular troublesome problem results from the invasion of the resininto the pores of the formation sand, where it causes a permeabilityimpairment at the formation sand/gravel interface. At such interfacesthe relatively large grains of the pack sand or gravel are pressedagainst the relatively small grains of the reservoir formations, andonly a small invasion of a gelled or semi-gelled or partially-curedresin may drastically reduce the permeability of the relatively smallpores of the reservoir sand.

Resin-forming polyepoxides suitable for use in the present inventioncomprise polyepoxides possessing more than one vicinal epoxy group permolecule. As discussed in the 166 patent, such polyepoxides may besaturated or unsaturated, aliphatic, cycloaliphatic, aromatic orheterocyclic.

Amines suitable for use as curing agents in the present process comprisethose capable of acting as both surface active materials which impartpreferential wetting properties to a solution of the resin-formingcomponents and as curing agents for converting the polyepoxides toinsoluble, infusible solid resins. As discussed in the 166 patent,preferred curing agents contain a plurality of amino nitrogen atoms thatare each attached to at least one hydrogen atom. Such amines includealiphatic, cycloaliphatic, aromatic, or heterocyclic polyamines andderivatives of such amines that contain the specified amino hydrogenatoms.

Solvents suitable for use in the present invention are semi-polarliquids or mixtures of liquids capable of keeping the unreacted andself-curing, partially-cured resins in solution until the solution hasbeen pumped into a subterranean location, and then allowing theself-curing, partially-cured resins to precipitate. As discussed in the166 patent, a particularly suitable solvent comprises a liquid mixtureof aromatic and non-aromatic hydrocarbons containing at least about 50%by volume of aromatic hydrocarbons in a proportion sufficient tomaintain the ungelled intermediate resin product in solution while thesolution is being transported to a subterranean region and then causethe precipitation of a somewhat further gelled intermediate resinproduct within a relatively few hours (such as about 2-12 hours) at thereservoir temperature (when the resin-forming solution is relativelydilute, e.g., the concentration of the resin-forming components in thesolution is from about 5-20% by volume).

As known to those skilled in the art, and as is further discussed in the166 patent, such epoxy-resin-forming solutions can advantageouslycontain additional components such as polymerization accelerators,polymerization retarders, or the like, to modify or control the initialresin separation time and/or subsequent curing time, etc. Suitableaccelerators comprise phenols, phenolic compounds, salicylic acid, andthe like. Suitable retarders comprise ketones such as acetone and itslower homologs. Where desirable, resin-to-sand bond strength enhancingagents, such as epoxy- or amino-functional silanes or the like, can beincluded within the solution.

Where it is desirable to inject a significant volume of theresin-forming solution into an oil-containing reservoir formation (whichusually also contains water) to consolidate a significant volume of thereservoir sand, pre-flush solutions are preferably injected to displaceoil and water from the zone to be treated. The oil-displacing solutionis a liquid oil solvent having significant miscibility with thereservoir oil. Diesel oil and/or mixtures of diesel oil and kerosenecontaining significant proportions of aromatic hydrocarbons areparticularly suitable oil-displacing fluids. Water-displacing fluidspreferably comprise liquids which are miscible with both oil and water,such as the lower alcohols, an oil solvent of a cationic surfactant, alower ketone such as acetone, or the like.

Oil-soluble viscosity-increasing polymeric materials suitable for use inthis invention comprise such oil-soluble polymers which aresubstantially completely soluble in the resin-forming solutions whenthey are initially prepared and also when they contain significantproportions of dissolved intermediate, self-curing partially-cured epoxyresin. Particularly suitable oil-soluble viscosity-increasing polymershave molecular weights in the range of from about 50,000-1,000,000.Examples of such polymers include isoprenestyrene copolymers,polyisobutene polymers, polymethacrylate polymers, olefinic copolymers,and synthetic rubbers such as butadiene-styrene copolymers. Theisoprene-styrene copolymer, SHELLVIS-50 (available from Shell) is aparticularly suitable thickening agent which exhibits a good shearresistance and is thermally stable at temperatures up to about 250° C.It has been found that polymer-containing resin-forming solutionscontaining about 15% by volume epoxy-resin forming components can besuitably thickened to effective viscosities of about 95 centipoises at23° C., and 65 centipoises at 70° C., when the concentration ofSHELLVIS-50 is about 7 grams of the polymer per 90 milliliters of thesolution. Polyvinyl pyrolidone polymers are particularly suitable forthickening resin-forming solutions and/or pre-flush liquids whichcomprise or contain a lower alcohol such as isopropyl alcohol. Ingeneral, the concentration of the viscosity increasing polymer ispreferably from about 20 to 70 grams per 100 milliliters of solution.

Where preflushes are used it is preferable that each fluid beinginjected has an effective viscosity at least equaling that of the fluidin the well borehole or reservoir to be displaced by the fluid beinginjected. In a particularly preferred sequence, diesel oil containingsufficient SHELLVIS-50 polymer to provide an effective viscosity atleast equaling that of the reservoir oil is injected to displace oil.Isopropyl alcohol containing sufficient polyvinyl pyrrolidone to providean effective viscosity to at least equaling that of the injected dieseloil solution is injected to displace the latter. A spacer fluidconsisting of a solution of aromatic and non-aromatic hydrocarbons andsufficient SHELLVIS-50 polymer to provide a viscosity at least equalingthat of the isopropyl alcohol solution is injected to displaced thelatter. And, then an epoxy-resin-forming solution containing sufficientSHELLVIS-50 polymer to provide an effective viscosity at least equalingthat of the spacer fluid is injected to displace the latter and effectthe consolidation treatment.

When the present invention is used for installing a consolidated mass ofgranular particles within a selected location, such as a downholeportion of a well borehole or fracture in a subterranean earthformation, the use of the present relatively viscous solution ofsignificant but relatively low proportions of resin-forming componentsavoids many of the disadvantages of the previously proposed proceduresfor conducting such operations. Epoxy-resin-forming solutions containingabout 15% by volume of resin-forming agents, about 70 grams ofSHELLVIS-50 polymer, about 1800 grams of sand grains (having an averagegrain size of about 1 millimeter) per liter of solution, and a mixtureof liquid aliphatic and aromatic hydrocarbons, provide suspensions whichare stable for a period of at least several hours at room temperature.The compressive strengths of consolidated masses of sand grains formedby such solutions have been found to be only slightly less than thoseconsolidated with the same type of solution with the SHELLVIS-50 polymeromitted.

In using the present process to install a sand or gravel pack no specialmeasures need to taken to prevent the carrying and consolidating liquidfrom entering the pores of a subterranean earth formation surrounding awellbore or fracture. The relatively low concentration of resin-formingmaterials ensures that the permeability of the earth formation will notbe unduly impaired, even in a formation of relatively low permeability.In a particularly preferred procedure, such a thickened resin-formingsolution is preceded by a slug of buffer liquid, preferably onecomprising a substantially equally-thickened portion of substantiallythe same viscosity as the resin-forming solution, but free of theresin-forming components. In forming consolidated masses offracture-propping particles, such a buffer is preferably spotted betweenthe slurry of propping particles in the resin-forming solution and anyfracturing fluids, and/or fracture acidizing fluids, or the like fluids,which are injected ahead of that particle-containing slurry. In general,in forming the consolidated masses, the slurries of particles inthickened resin-forming solutions are preferably injected into theborehole or fractures until the suspended particles are screened-outagainst the walls of the borehole or fracture. Suitable procedures andequipment for injecting slurries of packing or propping particles tocauses such "sand-outs" are well known and readily available to thoseskilled in the art. In using the present process, each slurry ofparticles in a thickened resin-forming solution is preferably followedby a slug of a similarly thickened resin-forming solution free of theparticles. When a sand-out is obtained, the injecting of fluid ispreferably interrupted for a time sufficient to allow a precipitatingand curing of the resin within the pores of the gravel pack or mass ofpropping particles, and, where the surrounding earth formation ispermeable, also within the pores of the surrounding earth formation.

Laboratory tests have been conducted to study the stability of thedisplacement of a reservoir fluid at various ratios of ##EQU1## withvarious injection rates (of the displacement fluid). The testeddisplacement fluids consisted of liquid compositions comprising mixturesof various amounts of "SHELLVIS"-50 oil-soluble polymer in anepoxy-resin-forming solution. That solution ("Fluid A") consisted ofequal parts by volume of the following three components:

(1) a xylene solution containing 34.2%vol "EPIKOTE" 828 epoxy resin and0.75 %vol "Dow Corning Z-6040" silane;

(2) a solution of "DDM" amine curing agent in a solvent mixturecomprising:

11.4 %vol of the curing agent,

20 %vol acetone,

6 %vol isopropyl alcohol, and

62.6 %vol xylene; and

(3) a solvent mixture of (in parts by volume) 31 parts xylene, 69 partskerosene and 33 parts of a solution containing 175 g phenol and 150 mlmetacresol per cash 190 ml xylene and 500 ml kerosene.

In "Fluid A" the concentration of the resin-forming components was about15% by volume.

FIG. 1 shows schematically (in perspective view) a transparent box 1used for visualizing the displacement of a reservoir formation fluid byvarious treating compositions.

The box dimensions were:

A=22 cm

B=8 cm

C=5 cm

D=30 cm

The opening 2 in the left vertical wall of the box had a diameter of0.08 cm and simulated a perforation in a well casing. A vertical screen3 consisting of a perforated plate with a small wire netting (200 mesh)allowed horizontal fluid flow in a pack 4 of crushed glass particles(average size 200 m m). The walls of the box were made of transparentmaterial to allow study of the flow of a dyed displacement fluid thatwas injected through opening 2 into the interior of the box 1 fordisplacing a reservoir or formation fluid present in the pore space ofthe pack 4 toward the screen 3. After passing through the screen, thedisplaced fluid was removed from the box via opening 5.

The fluid representing the formation fluid in the pore space of the boxwas ONDINA oil (consisting of paraffinic hydrocarbons) having aviscosity of 25 cP at the test conditions.

Four displacement tests were carried out at room temperature with FluidA mixed with the indicated proportions of SHELLVIS-50 polymer.

    ______________________________________                                                              Apparent                                                                      viscosity   Displacement                                Test Fluid A          at 51 sec. .sup.-1                                                                        rate cm.sup.3 /sec                          ______________________________________                                        1     + 20 g SHELLVIS/liter                                                                          13 cP      2.5                                         2    + 50 g SHELLVIS/liter                                                                           40 cP      2.5                                         3    + 70 g SHELLVIS/liter                                                                          120 cP      2.5                                         4    + 70 g SHELLVIS/liter                                                                          120 cP      1.0                                         ______________________________________                                    

FIG. 2 shows a side view of the box 1 of FIG. 1, wherein the boundarylines 6 indicate the position of the displacement front between theformation fluid and the treating fluid of test 1 at subsequent timeintervals. FIG. 3 shows the various positions of the displacement frontwhen applying an increased amount of viscosifying agent (test 2),whereas FIG. 4 shows the positions of the displacement front at a stillgreater amount of viscosifying agent (test 3). FIG. 5 shows thedisplacement of the reservoir fluid when using the same treating fluidas in test 3, but at a considerable lower injection rate.

The tests indicated that the displacement becomes more stable and lessfingering if the treating composition contained the higherconcentrations of the viscosifying agent, such as those of tests 3 and4. The increased uniformity of reservoir fluid displacement will resultin the absence of weak spots in a formation which is consolidated by aso-viscosified resin-forming solution.

Tests were made of the effect of the viscosifying agent SHELLVIS-50polymer on the compressive strength of the sand grains consolidated by aresin-forming solution containing various amounts of SHELLVIS-50. Packsof sand particles resembling a subterranean earth formation sand weremade in glass vessels. Silver sand (a well-washed silica sand) was usedfor this purpose, and each pack had a permeability of about 8 darcies.Subsequently the packs were flushed with treating fluids consisting ofthe above Fluid A having added thereto 2, 4 and 6 grams "SHELLVIS"-50polymer per 100 ml, respectively. After curing each pack for one nightat 65° C., the consolidated cores thus obtained were each cut into threepieces. The unconfined compressive strengths of the pieces are listed inthe following table:

    ______________________________________                                                           Unconfined                                                                    compressive strength                                       "SHELLVIS"-50 concentration                                                                      kg/cm.sup.2                                                8/100 ml           top      middle   bottom                                   ______________________________________                                        0                  not      185      not                                                         deter-            deter-                                                      mined             mined                                    2                  165      163      165                                      4                  190      185      175                                      6                  150      170      150                                      ______________________________________                                    

The tests indicate that when a concentration of 6 g "SHELLVIS"-50 per100 ml is dissolved in an epoxy-resin-forming treating fluid such asFluid A, the compressive strength of a granular earth formationconsolidated by that fluid is substantially unaffected.

In general, where it is desirable to benefit from using a givenepoxy-resin-forming solution that is relatively viscous, tests should bemade to correlate the treatment design with respect to the extent towhich the resin-forming and precipitating properties of the solutionwill be affected by the amount of a particular oil-soluble viscosityincreasing resin that would be needed to provide a particular viscosity.Where necessary, adjustments should be made regarding the kind andamounts of epoxide, as described in the 166 patent; and, alternativelyor additionally, a different thickener should be used and/or changesmade in the contemplated rates, volumes or compositions of fluids to beinjected, in order to avoid a significant degradation of theresin-forming and precipitating properties of the resin-formingsolution. In particular, the composition of the solution is adjustedwith respect to the temperature, injectivity and fracturing pressure ofa subterranean reservoir to be treated, so that the proportions ofaromatic and non-aromatic hydrocarbons and oil-soluble polymer in thesolution provide (a) an effective viscosity at which the solution can beinjected into the reservoir at a selected rate in response to a pressureof less than the reservoir fracturing pressure, and (b) a capability ofkeeping in solution the partially-cured epoxy resin that is formingwhile the solution is being injected into the reservoir at the selectedrate.

What is claimed is:
 1. An epoxy resin-forming solution which consistsessentially of:from about 5 to 30% by volume of a mixture of at leastone epoxy resin having more than one vicinal epoxy group per moleculeand at least one amine capable of curing that epoxy resin; said resinand amine being dissolved in a mixture of aromatic and non-aromatichydrocarbons containing at least about 50% by weight aromatichydrocarbon in proportions capable of maintaining a self-curingpartially-cured epoxy resin in solution while the solution is pumpedinto a subterranean location and then precipitating a self-curingpartially-cured epoxy resin; and, also dissolved in said mixture ofhydrocarbons, sufficient oil-soluble isoprene-styrene copolymer toincrease the effective viscosity of the solution to from about 1 to 150centipoises at from about 20° and 120° C., as measured at a shear rateof 51 reciprocal seconds in a Fann viscosimeter.
 2. The composition ofclaim 1 in which the effective viscosity of the solution is at leastabout 50 centipoises and particulate solids are suspended in thesolution.
 3. The composition of claim 2 in which the suspended particleshave an average diameter of about 1 millimeter.
 4. The solution of claim1 in which:the composition of the solution is adjusted with respect tothe temperature, injectivity and fracturing pressure of a subterraneanreservoir to be treated, so that the proportions of aromatic andnon-aromatic hydrocarbons and oil-soluble polymer in the solutionprovide (a) an effective viscosity at which the solution can be injectedinto the reservoir at a selected rate in response to a pressure of lessthan the reservoir fracturing pressure, and (b) a capability of keepingin solution the partially-cured epoxy resin that is forming while thesolution is being injected into the reservoir at the selected rate.